Mark Twain was right-handed, but I don't know about Clara and Jean.  I also
don't know about the cultural ways people drank from cups in those days.

I wonder who the young man is who comes into frame to give Clara a hat?

I think I might be able to speak to why the images vary so in darkness and
lightness.  In the early days of film there was no technical way to
copyright them as a complete moving image.  So Edison devised a way of
printing each frame of a film onto paper (many frames per page) and sending
copies of the papers to the Library of Congress to be copyrighted.  In fact,
the paper copies of the films are usually the only surviving copies in
existence from that era.  So, when you see an early Edison film, what you
are likely seeing is a re-filming frame by frame of the original paper
copies.  Unfortunately, those paper copies over the years have darkened in
places, making for very uneven frame contrasts.  I don't know that this is
the case with the Mark Twain film, but it looks as though it would be.  I
would guess that it could be cleaned up somewhat, but not really restored to
pristine quality.  I'd love to see a pristine digital copy of that film, not
only because it is the only film I know of of Mark Twain, but also because
it is the only film I know of of Jean, who appears to be young and happy and
vigorous in it.  I like to see that.

I think it's important to point out that it is extremely unlikely that
Edison THE MAN filmed Mark Twain and his daughters at Stormfield.  Rather,
it would have been an employee of Edison THE COMPANY.  I don't know that
Edison himself ever actually recorded a film or even had much to do with the
development of motion pictures, although he is often credited with
"inventing" them.  By the late 1880s, when motion pictures were first
recorded on film and paper, he had employees who did the actual work of
inventing and developing projects and systems.  He also simply bought the
work of other individuals outright and put his name on it.

Does anyone know if there are any other surviving motion pictures of Clara,
or recordings of her voice?  Or of her daughter?

Carl